Spotting rifles have been used for larger bore guns and rocket devices for several years. The advent of the ballistically matched spotting round has greatly reduced the difficulty and time required to align the spotting charge impact with the main tube round. However, even with ballistically matched spotting rounds in order to have the spotter trajectory approach as closely as possible the larger weapon, it is necessary to have a very accurate alignment of the spotter rifle barrel with the main tube. Typically this alignment requires multiple adjustments to the spotter weapon where it attaches to the rocket launcher tube. A preferred solution is to adjust the barrel of the spotting rifle without having to relocate the entire spotting rifle in relation to the main tube or main rifle. A problem has developed however in previous attempts to move the barrel while maintaining a fixed receiver in that gaps or misalignments occurred while moving the barrel at the receiver end. Also, during firing of the weapon, the increased heat and the expansion of the barrel can cause a misalignment. A simple geometry is needed that will allow a single point adjustment of the barrel and which will also maintain a sealed mating surface between barrel and receiver of the spotting rifle. Also, it is desired to accommodate heat-induced expansion of the spotter rifle barrel without causing any misalignment.